I. Field of the Invention
This invention relates to a multiple wall chimney formed of a plurality of chimney sections connected together and, in particular, to an expansible spacer ring positionally captured between the walls of the chimney sections to maintain the flow-through spacing of the walls.
II. Description of the Prior Art
Double-walled metal chimneys have been widely used in place of masonry chimneys because of their versatility particularly in joining chimney sections to form the desired chimney length. The double wall reduces heat conduction to the exterior of the chimney permitting the chimney to be mounted without the threat of combustion of supporting materials. The double wall also ensures that smoke and gases are vented through the chimney even if some leakage occurs through the inner wall. Spacer members are mounted between the walls so as to minimize heat conduction from the inner wall to the outer wall while also not blocking the annulus therebetween to allow the flow of gases upwardly through the annulus.
The chimney sections are normally constructed by positioning the spacer elements between the wall segments and securing the elements to the inner and outer walls. The spacers may be spot welded, riveted, or bolted to the wall segments. However, the secured spacer elements do not provide any leeway for expansion and contraction during operations. Moreover, attachment of the individual spacer elements raises the cost of production.
As a substitute for the individual spacer elements, spacer rings have been developed for insertion between the walls of the chimney sections. Such spacer rings may be an annular ring with spacer elements attached thereto or cut and bent out of the ring itself During assembly, the ring is secured between the wall sections in much the same manner as the individual elements. Although simplifying manufacture by incorporating the spacer members into a ring for simultaneous insertion, manufacturing costs are not substantially reduced since the spacer ring must still be secured between the walls to prevent longitudinal shifting.
Corrugated or sinusoidal spacer bands have also been developed to maintain the spacing between wall sections. Typically, these spacers are formed of a continuous band having its ends joined to form a ring. The corrugated spacer ring is thereafter secured between the walls by spot welding the peaks of the spacer to the wall which they contact. Although simplifying positioning, manufacturing costs are not substantially reduced since the ring must be secured to the wall sections. The ring also does not allow for expansion and contraction in relation to the wall sections. However, the strength of the corrugated spacer ring is greater than the other spacer means thereby providing structural strength to the double-walled chimney.